PFT Results Explained: A Safety Manager's Guide to FVC, FEV1, and Ratios

A pulmonary function test report lands on a safety manager's desk with a page of numbers, a curve, and a classification the lab or physician already assigned. You don't need to diagnose anything — that's the reviewing physician's job — but you do need to know what the report is telling you well enough to ask the right follow-up question, flag a trend, and explain a result to an employee who's asking what it means.

What do FVC and FEV1 actually measure?

FVC (forced vital capacity) is the total volume of air an employee can forcefully exhale after a maximum inhale — it's a measure of lung size and how much air moves in and out. FEV1 (forced expiratory volume in one second) is the volume exhaled in just the first second of that same maneuver — it's a measure of how fast air moves out, which is where airway obstruction shows up first. Both numbers come from the same forced exhalation, captured on the same flow-volume curve, but they answer different questions: FVC asks "how much," FEV1 asks "how fast." A technician can't get a valid FEV1 without a valid FVC maneuver behind it, which is why curve acceptability matters before either number gets interpreted at all.

What does the FEV1/FVC ratio tell you?

The FEV1/FVC ratio — FEV1 divided by FVC, expressed as a percentage — is the single most useful number on the report for telling obstructive patterns apart from restrictive ones. A normal ratio is roughly 70-80% or higher depending on age and the reference equations used. A low ratio (air moving out slowly relative to total volume) points toward an obstructive pattern, like the kind seen in asthma or COPD. A normal or even high ratio paired with a low FVC points toward a restrictive pattern, where lung volume itself is reduced but airflow isn't obstructed. The ratio doesn't diagnose either condition on its own, but it tells the reviewing physician which direction to look, and it's usually the first thing they check on the report.

Obstructive vs restrictive: what's the practical difference?

Pattern	FVC	FEV1	FEV1/FVC ratio	Common context
Normal	Normal	Normal	Normal (≥70-80%)	No flagged abnormality
Obstructive	Normal or reduced	Reduced (more than FVC)	Reduced	Asthma, COPD, some occupational airway exposures
Restrictive	Reduced	Reduced (proportionally)	Normal or elevated	Some interstitial or chest-wall conditions, reduced effort
Mixed	Reduced	Reduced (more than proportional)	Reduced	Combination pattern, needs physician review

What is "percent predicted" and why does it matter more than the raw number?

A raw FVC or FEV1 in liters means little on its own — a 25-year-old and a 60-year-old have very different normal lung volumes even with identical health. Percent predicted compares an employee's actual result against a reference value calculated from their age, height, sex, and sometimes race, using standardized reference equations (commonly NHANES III or the Global Lung Function Initiative tables). A result at 100% predicted matches the reference population exactly; results are generally considered within normal limits above roughly 80% predicted for FVC and FEV1, though the exact cutoff varies by the reference set and reviewing physician's protocol. This is the number that actually gets compared over time — not the raw liters — because it already accounts for the demographic differences that would otherwise make longitudinal comparisons meaningless.

How should a safety manager read a longitudinal trend, not just one test?

A single test tells you where an employee stands today; a trend across annual tests tells you whether something is changing. A gradual decline in percent-predicted FEV1 across several years — even if each individual result still falls "within normal limits" — is exactly the pattern a medical surveillance program exists to catch before it becomes symptomatic. This is the same logic behind standard threshold shift tracking in hearing conservation: the year-over-year comparison against the employee's own baseline matters more than any single pass/fail cutoff. Flag a downward trend for physician review even when no single test crossed an absolute threshold, and keep every test's raw data alongside the report so a reviewing physician can actually see the trajectory, not just this year's summary line.

How Foster handles this

Our technicians run every spirometry session to ATS/ERS acceptability and repeatability criteria before a result ever reaches percent-predicted comparison — a technically invalid curve produces a number that looks precise and means nothing. Reports we deliver include the raw curve data plus the percent-predicted calculation against the reference set your medical review protocol specifies, and we flag any employee whose year-over-year trend is moving the wrong direction even when the current test is still in range. That data structure is what makes physician review fast instead of a re-read of raw numbers from scratch every cycle. See our full spirometry equipment and testing services, and if you're setting up or auditing an existing program, our on-site occupational health testing team can walk through your current reporting format directly.

FAQ

What FEV1/FVC ratio counts as normal?

Roughly 70-80% or higher, though the exact cutoff depends on age and which reference equations your medical review protocol uses — a ratio below that range generally points toward an obstructive pattern and should go to the reviewing physician.

Is a low FVC always a problem?

Not necessarily on its own. A single low FVC can reflect a genuine restrictive pattern, but it can also reflect submaximal effort, an incomplete exhale, or a technically unacceptable maneuver — which is why curve quality gets checked before the numbers get interpreted.

Why does percent predicted matter more than the liters number?

Because normal lung volume varies enormously by age, height, and sex. Percent predicted normalizes for those factors so a result — and a trend across multiple years — actually means something comparable.

Who decides whether a PFT result requires follow-up?

The reviewing physician or other licensed healthcare professional, not the safety manager or technician. A safety manager's job is to make sure the test was run correctly, the report reaches the reviewer, and any concerning trend gets flagged rather than filed.

How often should PFTs be repeated to build a useful trend?

Match whatever surveillance schedule applies to the exposure — commonly annual for standard occupational programs. The value of the trend comes from consistent timing and consistent technique test to test, not from any single interval being inherently correct.